Method for producing composite bodies of aluminum and sintered aluminum powder



Nov. 20,. 1962 H. HUG

METHOD FOR PRODUCING COMPOSITE BODIE mt, T W

INVENTOR f/qlvs Hugnite 3,065,073 Patented Nov. 20, 19fi2 lVlETHGD FUR PRGDUCING CDNLPOSITE BODIES F ALUMHIUM AND SINTERED ALUMENUM POWDER Hans Hug, Neuhausen am Rheinfall, Switzerland, assignor to Aluminium-minsnie-Aktien-Gesellschaft, Chippis (Switzerland), a joint-stock company of Switzerland Filed June 5, 195$, Ser. No. 818,433 Ilaims priority, application Switzerland June 9, 1958 8 Claims. (Ci. 75208) It is often desirable to have at disposal composite bodies which consist partly of wrought or cast aluminum or aluminum alloy and partly of sintered aluminum powder. This is especially the case with light metal pistons for engines. These pistons are exposed in service to high temperatures and are therefore made from heat-resisting alloys. Bodies made from sintered aluminum powder have proved to be very heat resistant. These sintered bodies are produced by powder metallurgy and are therefore more expensive than the usual wrought or cast alloys and, accordingly, for the reason of economy it is generally not practicable to make pistons wholly from sintered aluminum powder. In order to take advantage of the high heat-resistance of the sintered aluminum bodies efiorts have already been made to make only those parts of the piston from sintered aluminum powder which are exposed to high temperatures, namely the piston head and the zone of the piston-rings, and to manufacture the other parts of the piston from wrought or cast aluminum alloys. For this purpose inserts made from sintered aluminum powder have been disposed in the body of the piston by casting or pressing. But it proved to be very diflieult to obtain by these methods an intimate and unobjectionable bond between the insert and the surrounding parts of the piston.

It is an object of my present invention to eliminate the imperfection of the known methods and to produce composite bodies of aluminum and sintered aluminum powder with a satisfactory bond. In the following description the expression aluminum means unalloyed metal as well as aluminum alloys.

According to my invention aluminum powder is coldpressed onto a conventionally-produced (wrought or cast) piece of aluminum, whereafter the composite body is heated and sintered under pressure (sinter-pressed).

The cold-pressing is preferably carried out in a die in which one introduces first the wrought or cast piece of aluminum and which is then filled with aluminum powder. The aluminum powder is suitably a fiaky powder with an aluminum oxide content of at least 6% and a total grease content of less than 0.3%. Such a powder may be produced for example according to the method described in Patent No. 2,678,880 (British Patent No. 698,789, Japanese Patent No. 214,646), the aluminum oxide of the powder is formed during milling by oxidation of the powder particles and is not added as aluminum oxide powder to the aluminum powder.

The invention is described by way of example in the accompanying drawing, the figures showing different steps of the method. FIGS. 1 and 2 show in section the composite body before and after cold-pressing. FIG. 3 shows an engine piston obtained from a composite body made according to the invention. FIGS. 4 and 5 show in section the manufacture of a composite body with an annular insert before and after cold-pressing.

A cast or wrought piece 2 of aluminum or aluminum alloy (ie an aluminum metal) is introduced into the die 1. Then the calculated amount of aluminum powder 3 is filled in. The press ram 4, for example the ram of a drop forge, compresses the powder at room temperature to the compact 5 which becomes thereby already bonded to the piece 2. The cold-pressing is carried out under a pressure of for-example 1 to 4 t./cm. The piece 2 in the PEG. 1 has an annular shoulder. But it is also possible to use a piece with an otherwise shaped or a flat bonding surface. The bonding surface may be provided for example with projections or grooves in order to increase the bonding area between both parts.

The cold-pressed body is then wrapped to aluminum foil, heated slowly in a furnace to the sintering temperature and sinter-pressed at this temperature under a pressure of for example 5 to 8 t./cm. One obtains in this way the desired dense structure of the sintered part and an intimate bond between it and the cast or wrought part 2.

The composite body may be shaped afterwards, by forging or otherwise, for example to the engine piston shown in FIG. 3. This piston consists of a wrought part 6 of aluminum alloy and of a heat resistant part 7 of sintered aluminum. The forging operation results in a kneading of the whole body and increases especially the elongation of the sintered part of the composite piston.

FIGS. 4- and 5 show the way of applying an annular sintered part onto a cast or wrought body. In the die 1 a head piece 10 is placed on the cast or wrought body 8, which has a projection 9. The aluminum powder 11 is filled in around this headpiece. For the cold-pressing one uses a hollow press ram 12 which produces the compact 13. From this cold-pressed body one may manufacture by sinter-pressing and forging a piston having a pistonring zone of sintered aluminum.

In the described examples the forging operation follow the sinter-pressing. But it is also possible to carry out the forging together with the sinter-pressing in one step.

For the manufacture of the sintered part one must consider the general working conditions for the making of sintered alumintun bodies (see, for example, the article Sintered Aluminum Powder, by R. Irmann, Dr. Ing., appearing on pages 236-241 of Symposium on Powder Metallurgy, 1954, Special Report No. 58, published by The Iron and Steel Institute, 4 Grosvenor Gardens, London, SW. 1, and particularly the paragraph beginning Melting point in the right-hand column on page 238), but bearing in mind the properties of the cast or wrought part. If for example a sintered part must be bonded to a part made from an aluminum alloy, the sintering temperature must be below the lowest melting point of the alloy.

The cold-pressing of the composite body may be carried out by any process aplying a sufiicient pressure, not only by drop forging.

What 1 claim is:

l. A method of producing a composite body of sintered aluminum powder and an aluminous metal member formed originally by casting which comprises cold pressinf flaky aluminum powder under a pressure of not less than 1 t./cm. onto said aluminous metal member, applying heat to the composite body thus produced to raise it to a sintering temperature below the melting point of the aluminous metal, and subjecting the composite body to said sintering temperature under a pressure of not less than 5 t./cm.

2. A method as in claim 1 wherein the cold pressing step is carried out at a pressure of from 1 to 4 t./cm. and the sintering step is carried out at a pressure of from 5 to 8 t./crn.

3. The method according to claim 1, using a flaky aluminum powder having an aluminum oxide content of at least 6% and a total grease content of less than 0.3%.

4. The method according to claim 1, in which the cold-pressing is carried out in a die.

5. The method according to claim 1, in which the bonding surface of the a1un1inous body is provided with References Cited in the file of this patent grooves, in order to improve the bond.

6. The method according to claim 1, in which the bOnd- UNITED STATES PATENTS ing surface of the aluminous metal body is provided with 1,950,356 De Bats Mar. 6, 1934 projections. 5 1,989,186 De Bats Jan. 29, 1935 7. The method according to claim 1, in which the com- 2,044,853 Laise June 23, 1936 posite body is thereafter forged. 2,549,596 Hamilton et a1 Apr. 17, 1951 8. The method according to claim 1, in which the cold- 2,657,961 Lassberg Nov. 3, 1953 pressed body is subjected to sintering conditions under 2,796,660 Irrnann June 25, 1957 pressure by forging at high temperature. 1 2,809,891 Ennor Oct. 15, 1957 ,mAsm .4 km 5. Mt U UNITED STATES PATENT OFFICE QE 'HFECATE OF QQRECTIUN Patent No. 3 ,O65 O73 November 20, 1962 Hans Hug I It is hereby certified that e ror appears in the above numbered pat- I ent requiring correction and that the said Letters Patent should read as corrected below.

Column l line 67, for "aluminum" read aluminous column 2 11116354 and 55 for l "pressinf" read pressing column 3 line 1, before ."body'P insert meta Signed and sealed this 30th day of April 1963.,

(SEAL) Attest:

ERNEST w. SWIDER DAVID A Attesting Officer I Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,065,073 November 20, 1962 Hans Hug It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below,

Column 1, line 67, for "aluminum" read aluminous column 2, lines 54 and 55, for pressinf" read pressing column 3 line l before ."body" insert metal a Signed and sealed this 30th day of April 1963.,

(SEAL) Attesit:

ERNEST w. SWIDER DAVID LADD Attesting Officer I Commissioner of Patents 

1. A METHOD OF PRODUCING A COMPOSITE BODY OF SINTERED ALUMINUM POWDER AND AN ALUMINOUS METAL MEMBER FORMED ORIGINALLY BY CASTING WHICH COMPRISES COLD PRESSING FLAKY ALUMINUM POWDER UNDER A PRESSURE OF NOT LESS THAN 1 T./CM.2 ONTO SAID ALUMINOUS METAL MEMBER, APPLYING HEAT TO THE COMPOSITE BODY THUS PRODUCED TO RAISE IT TO A SINTERING TEMPERATURE BELOW THE MELTING POINT OF THE ALUMINOUS METAL, AND SUBJECTING THE COMPOSITE BODY TO SAID SINTERING TEMPERATURE UNDER A PRESSURE OF NOT LESS THAN 5 T./CM.2. 